1. Field of the Invention
The present invention relates in general to a composite ferrite sheet, a method of fabricating the composite ferrite sheet, and an array of sintered ferrite segments used for the composite ferrite sheet, and more particularly to a method of advantageously fabricating a flexible composite ferrite sheet which has a planar sintered ferrite layer divided into rectangular segments and which absorbs or blocks external electromagnetic waves incident upon electronic components or electromagnetic waves generated by the electronic components per se, or which is bonded to NFC devices or antenna coils to improve their communication performance or improve performance of non-contact type power transmission devices, and a method of advantageously manufacturing electromagnetic wave absorbing devices using the composite ferrite sheet.
2. Description of Related Art
JP-A-2009-99895 proposes an example of a laminated body that absorbs electromagnetic wave to be installed on an electronic component or an electronic device to absorb electromagnetic waves irradiated therefrom or incident thereupon. The laminated body for absorbing electromagnetic wave includes a planar ferrite layer consisting of a multiplicity of sintered ferrite segments regularly arranged in longitudinal and transverse rows so as to form a lattice structure, and sheet layers supporting the planar ferrite layer. This publication discloses a method of fabricating a laminated structure body by first firing a ferrite green sheet having a multiplicity of dividing grooves formed on its one surface so as to extend longitudinally and transversely, to prepare a sintered ferrite body in the form of a rectangular plate, then bonding a double-coated adhesive tape to one of the opposite surfaces of the sintered ferrite body and a protective tape to the other surface, and subsequently holding the sintered ferrite body in pressing surface contact with a curved surface of a rigid body, to regularly divide the sintered ferrite body longitudinally and transversely into mutually independent segments which are held in contact with each other, whereby the above-described laminated structure is fabricated such that the laminated structure as a whole is flexible.
While the publication discloses that a knife blade is used as means for forming a plurality of dividing grooves that divides the ferrite green sheet into the segments, the publication does not teach a specific manner of forming the dividing grooves in the ferrite green sheet with the knife blade such that the grooves have almost the same depth, and does not teach a manner of forming a multiplicity of dividing grooves at one time. Namely, the publication discloses only the use of the knife blade to form the dividing grooves, but never refers to techniques for improving the accuracy of formation of the plurality of dividing grooves, the efficiency of formation of the plurality of dividing grooves, and the productivity of the grooved ferrite green sheet.
JP-A-2008-296431 discloses a method of fabricating a ceramic sheet having a ceramic layer consisting of a plurality of ceramic segments arranged in a plane, by first forming a plurality of recesses or holes in a sintered ceramic body in the form of a thin plate by a laser beam machining such that the recesses or holes are spaced apart from each other along lines, and then breaking the thin sintered ceramic body along those lines, to obtain the ceramic segments, or by first forming a plurality of recesses or holes in a green ceramic body with blades or a die such that the recesses or holes are spaced apart from each other along lines, then firing the green ceramic body along those lines, to obtain the ceramic segments. However, the process disclosed in this publication requires a timing-consuming and cumbersome operation to form the plurality of recesses or holes along the lines, and accordingly has a potential problem in terms of the productivity of the desired ceramic sheet, and potential risk of difficulty to accurately break the thin sintered ceramic sheet along the lines of the recesses or holes, and generation of minute ceramic pieces upon breaking of the sintered ceramic sheet.
JP-A-2009-182062 discloses a method of fabricating a composite ferrite sheet by forming grooves in a grid pattern in a surface of a ferrite green sheet with a knife device, a laser machining device, or a die, to obtain a grooved ferrite green sheet used to form ferrite segments which constitute the composite ferrite sheet. However, this publication does not teach a specific manner of forming.
Registered Design No. JP1368549 proposes a sintered ferrite sheet to be installed on a wireless communication device to absorb or block electromagnetic waves. Although this publication discloses discontinuous longitudinal and transverse grooves formed in a surface of the sintered ferrite sheet, the publication does not teach a manner of forming the longitudinal and transverse grooves.